Car Stalling After A New Battery Is Fitted – Help & Advice

So you’ve bought a new battery to fix a starting problem, but now your car is stalling instead!

As cars have got progressively better, so have their electrical systems. More advanced systems are helpful, but their software can sometimes cause problems. Your car is equipped with a computer or ECU and sensors that help it run smoothly.

This adaptive memory is kept in your vehicle’s volatile random-access memory (VRAM).

And here lies the problem!

During the process of replacing your battery and your car’s computer systems is unplugged, there’s a chance that it’ll reset your car’s memory to factory default settings. Even if you have just unplugged the battery for a brief period, it may lose the data saved in the VRAM. This might contain idle engine settings, which could cause your vehicle to stall.

After the ECU’s VRAM resets, your vehicle must start learning all the settings it has been forced to forget. This can take time.  

I’m afraid many people will tell you to check all sorts of things when your car starts stalling after having a new battery fitted. The truth is many ignore the bit about having a new battery fitted and go off on a tangent explaining how it could be anything ranging from a clogged air filter to a dodgy fuel pump. The list goes on. These two parts could be, but it is unlikely if your car wasn’t stalling before the new battery was fitted.

You would expect the car shop to fix this for you after replacing the battery, but the reality is some won’t spend the time as there is little money in replacing batteries.

Many car shops will feel that if they include the labor time to fix this issue after the battery has been fitted, a customer will take a cheaper quote from a mechanic who won’t mention the reset.

So now we have narrowed down the new battery stalling problem to be ECU memory-related; let’s look at ways that you can get the ECU to relearn the correct idle speed for your car.

There are a couple of ways to do this, and I think that each way is best described visually. I have included two videos that show the two methods that I know.

In reality, even without trying these two methods, your car’s ECU will relearn the correct idle speed after being left idle for a while.

How To Stop A Car from Stalling After A Battery Change

The first method works well for Honda stick shift cars. However, when you watch the video, you’ll see that the steps are almost universal to any car.

This is the key to getting it right.

• Make sure that the ECU isn’t holding memory. If you’ve been driving and your car stalling, it may have been relearning with bad information. You may need to disconnect and reconnect the battery to ensure it’s clean.
• Make sure all electrical components and systems are off.

https://youtu.be/dUMDzCvONTs

• Start the car and get it warm and up to operating temperature. Revving the car will do this quickly. If your car has a temperature gauge, it’s within its operating temperature once the needle leaves the blue section. In more modern cars, a blue thermometer light shows the car is cold but will disappear once the car warms up.
• Once you’re happy, it’s warm, let the car idle. It should remain steady and below 1000 RPM. Every car make idles at different speeds, so it’s difficult to be more precise.
• Take the car for a drive and make sure it has stopped stalling. If not, return home and try this procedure again.
• If this doesn’t fix it, you may have to search for specific information about your make and model of car or speak with the dealer for guidance.

Here is the second method for an automatic transmission car.

It’s a similar procedure but with a few tweaks.

• Ensure the handbrake is off and the car is in Park
• Turn the ignition key twice but only start the car on the second turn.
• Pull the handbrake, and put the car into drive with your foot on the brake.
• Keep your foot on the brake at all times.
• Wait until the car gets up to operating temperature.
• The needle may dance around but should settle below 1000 RPMs

https://youtu.be/xJkQjVKy1yY

While your vehicle can relearn its parameters, avoiding the problem is a far better solution. Fortunately, there is an easy way to maintain your ECU data.

It is possible to store your vehicle’s settings using a memory saver, which plugs directly into a power source or cigarette lighter adapter. It’s like a flash drive for your car.

What Is a Car Memory Saver?

A memory saver for your car battery is a memory stick with a small battery.

When the primary battery is replaced, this device will keep all of your car’s computer memory stored safely. It’s an invaluable time-saving gadget.

It may be too late to get used out of this, but as these devices have a battery life of over five years, it is worth having one handy for the next time you have to replace your car battery.

Sooner or later, the time will come when you’ll need to replace your car’s battery again. The average car battery lasts 3 to 5 years, so it’ll need changing sooner than you think.

It’s not just the RPM idle speed that is stored, either. You may have found or will shortly that you’ve lost the pre-sets on electric seats and radio stations from stereo systems too. The clock and date will be wrong too.

There could be more systems as well. The more modern and luxurious your car is, the more info you’ve likely lost by replacing the battery.

Your car will be able to relearn some of that information. But some systems will need to be reprogrammed depending on the car you drive.

Other Stalling Causes After A New Battery

As mentioned above, the most likely cause is that the ECU needs to relearn the correct idling speed.

If that doesn’t work, then here are the other reasons. These are not caused by the battery being changed and are purely coincidental.

These are more likely reasons if you have noticed tell-tale signs before changing the battery or haven’t had your car tuned regularly. If your engine isn’t getting the right fuel/air mixture, it can idle rough and stall.

The one reason that stands out is a disconnected vacuum hose. This can be pushed out of the way on some cars to access the battery.

This is easy to check.

https://youtu.be/UL9NqqZToJs

Other causes of rough idle and stalling include:

• Old Spark Plugs or Coils
• Clogged Fuel Filter
• Clogged Oil Filter
• Bad Fuel Pump
• Fuel Injectors Clogged
• Bad Idle Speed Control Valve

In Conclusion

If your car’s computer systems are unplugged while changing the battery, your car’s memory might be reset to the factory default settings. The car VRAM could lose the information it had saved. This will include settings for the idle engines, which could cause your car to stop.